Image pickup apparatus

ABSTRACT

An image pickup apparatus which makes it possible to achieve reduction of the size in the optical axis direction thereof, and easily maintain the accuracy of rectilinear guidance between lenses. A cam barrel rotatable around an optical axis has a cam for controlling motion of a lens unit along the optical axis. A rectilinear motion guide unit rectilinearly guides the lens unit. The rectilinear motion guide unit has a rectilinear motion barrel fitted in the cam barrel for rectilinearly guiding the lens unit, and a rectilinear motion member that is rectilinearly guided by a rectilinear motion guide member disposed around the rectilinear motion barrel and is connected to the rectilinear motion barrel. The cam barrel is sandwiched from front and rear in a direction along the optical axis by the rectilinear motion guide unit, and is movable together therewith along the optical axis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup apparatus, and more particularly to an image pickup apparatus characterized by its zoom mechanism.

2. Description of the Related Art

Conventionally, there have been proposed various techniques concerning a zoom lens barrel which is extended from the body of an image pickup apparatus for shooting and retracted into the apparatus body for accommodation. This type of zoom lens barrel is formed by combining a plurality of rectilinear motion barrels and rotary barrels, and is configured to be advanced and retracted along an optical axis direction. Further, when the image pickup apparatus is not in use, these barrels are retracted, whereby the thickness of the main unit of the image pickup apparatus is reduced.

In such a retractable lens barrel, when cams are formed in cam barrels, it is required to lay out the respective shapes of cams such that they do not interfere with each other. Further, it is required to provide a rectilinear motion guide in each of lens units.

In a lens barrel mechanism disclosed in Japanese Patent No. 3842087, a rotary barrel is formed with cams on outer and inner surfaces thereof such that the cams do not cross each other. Therefore, without providing a dedicated cam barrel for each of lens units, it is possible to move each lens unit in an optical axis direction using the single rotary barrel which is short in length. Further, rectilinear motion barrels for rectilinearly guiding the lens units, respectively, are rectilinearly guided by a fixed barrel, and hence they are not required to be engaged with each other. This contributes to reduction of the size of the lens barrel mechanism.

In a lens barrel formed by a combination of cam barrels and rectilinear motion barrels, including the lens barrel mechanism disclosed in Japanese Patent No. 3842087, generally, each cam barrel and each rectilinear motion barrel associated therewith are caused to move in unison in the optical axis direction. To cause the cam barrel and the rectilinear motion barrel to move in unison in the optical axis direction, in the above-described example, a projection is formed on one of the barrels and a groove is formed on the other, for example, whereby the two are caused to move in unison when they come to a predetermined phase. By providing such a so-called bayonet mechanism, the cam barrel and the rectilinear motion barrel are caused to move in unison in the optical axis direction.

However, this mechanism prevents cams from being laid out in a manner extending across the surface of the cam barrel, which is a hindrance to the reduction of the size of the lens barrel in the optical axis direction.

Further, in the lens barrel mechanism disclosed in Japanese Patent No. 3842087, the rectilinear motion barrels for rectilinearly guiding the lens units, respectively, are rectilinearly guided by the fixed barrel independently of each other. However, since the lens units are guided by the respective linear motion barrels which are independent of each other, it is difficult to maintain the accuracy of rectilinear guidance between the lenses.

SUMMARY OF THE INVENTION

The present invention provides an image pickup apparatus which makes it possible to achieve reduction of the size in the optical axis direction thereof, and easily maintain the accuracy of rectilinear guidance between lenses.

The present invention provides an image pickup apparatus comprising a lens unit that is configured to move along an optical axis, a rectilinear motion guide unit that is configured to rectilinearly guide the lens unit, a rectilinear motion barrel that is configured to rectilinearly guide the lens unit, a rectilinear motion member that is configured to be rectilinearly guided by a rectilinear motion guide member disposed around the rectilinear motion barrel and is connected to the rectilinear motion barrel, and a cam barrel that is sandwiched from front and rear in a direction along the optical axis by the rectilinear motion guide unit, the cam barrel being movable together with the rectilinear motion guide unit along the optical axis, the cam barrel relatively rotating with the rectilinear motion guide unit, and the cam barrel being formed with a cam for controlling motion of the lens unit along the optical axis.

According to the image pickup apparatus of the present invention, it is possible to achieve reduction of the size in the optical axis direction thereof, and easily maintain the accuracy of rectilinear guidance between lenses.

The features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a lens barrel of an image pickup apparatus according to a first embodiment of the present invention, which is in a wide-angle state when the image pickup apparatus is in a shooting mode.

FIG. 2 is a view of the lens barrel of in the telephoto state when the image pickup apparatus is in the shooting mode.

FIG. 3 is a view of the lens barrel in a retracted state.

FIG. 4 is an exploded perspective view of the lens barrel.

FIG. 5 is a perspective view of the image pickup apparatus.

FIG. 6 is an exploded perspective view showing a rotary barrel and a fixed barrel of the lens barrel shown in FIG. 4.

FIG. 7 is an exploded perspective view of a first intermediate barrel unit of the lens barrel shown.

FIG. 8 is an exploded perspective view of a second intermediate barrel unit of the lens barrel shown.

FIG. 9 is an exploded perspective view of a cam barrel unit of the lens barrel.

FIG. 10 is an unfolded view showing the inner peripheral surface of the fixed barrel appearing in FIG. 6.

FIG. 11 is an unfolded view showing the inner peripheral surface of a first intermediate rectilinear motion barrel appearing in FIG. 7.

FIG. 12 is an unfolded view showing the inner peripheral surface of a second intermediate rectilinear motion barrel appearing in FIG. 8.

FIG. 13 is an unfolded view showing the inner peripheral surface of a cam barrel appearing in FIG. 9.

FIG. 14 is a view of a lens barrel of an image pickup apparatus according to a second embodiment of the present invention, which is in the wide-angle state when the image pickup apparatus is in the shooting mode.

FIG. 15 is an exploded perspective view of a fixed barrel and a gear unit of the lens barrel.

FIG. 16 is an exploded perspective view of a first intermediate barrel unit of the lens barrel.

FIG. 17 is an unfolded view showing the inner peripheral surface of the fixed barrel appearing in FIG. 15.

FIG. 18 is an unfolded view showing the inner peripheral surface of a first intermediate rectilinear motion barrel appearing in FIG. 16.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will now be described in detail below with reference to the accompanying drawings showing embodiments thereof.

FIG. 1 is a view of a lens barrel of an image pickup apparatus according to a first embodiment of the present invention, which is in the wide-angle state when in the shooting mode. FIG. 2 is a view of the lens barrel in the telephoto state when the image pickup apparatus is in the shooting mode. FIG. 3 is a view of the lens barrel in a retracted state. FIG. 4 is an exploded perspective view of the lens barrel. FIG. 5 is a perspective view of the image pickup apparatus.

As shown in FIG. 5, the present image pickup apparatus (camera) has a lens barrel (barrel unit) 2 mounted to a camera body 1.

As shown in FIGS. 1 to 3, the lens barrel in the present embodiment is comprised of four photographic lens units. A first group lens (first lens unit) 11 is held by a first group barrel 61, a second group lens (second lens unit) 12 by a second group holder 72, and a third group lens 13 by a third group holder 73. Further, a fourth group lens 14 is held by a fourth group holder 74. The fourth group lens 14 is configured such that it is movable along an optical axis by receiving a driving force from a drive source, not shown.

The lens barrel has a four-stage structure, and is capable of changing its entire barrel length between a shooting state and a retracted state.

Now, a description will be given of each stage of the lens barrel.

A fixed barrel unit 20 is comprised of an outer barrel cover 21, and a rotary barrel 22 and a fixed barrel 23 disposed radially inward of the outer barrel cover 21. The barrel cover 21 is secured to the camera body 1 e.g. with screws and held thereby, together with the fixed barrel 23 and a holder 24 for holding an image pickup element 15.

FIG. 6 is an exploded perspective view showing the rotary barrel and the fixed barrel of the lens barrel shown in FIG. 4.

The barrel cover 21 holds a zoom gear unit 80 appearing in FIG. 6. The zoom gear unit 80 is comprised of a motor 81 as a drive source and gears 82 to 86 for transmitting a driving source from the motor 81.

The gear 86 is in meshing engagement with a gear 22 g of the rotary barrel 22, and the rotary barrel 22 rotates about the optical axis circumferentially along the outer peripheral surface of the fixed barrel 23. The fixed barrel 23 has an inner peripheral surface thereof formed thereon with straight advance grooves 23 s, through grooves 23 k, and cam grooves 23 c. The rotary barrel 22 has an inner peripheral surface thereof formed thereon with straight advance grooves 22 s.

FIG. 7 is an exploded perspective view of a first intermediate barrel unit 30 of the lens barrel shown in FIG. 4.

The first intermediate barrel unit 30 as a first stage of the lens barrel is comprised of a first intermediate rotary barrel 31 and a first intermediate rectilinear motion barrel 32.

The first intermediate rectilinear motion barrel 32 has a projection 32 b for engagement with a groove portion 31 b (see FIG. 1) formed circumferentially on the inner periphery of the first intermediate rotary barrel 31, so that the intermediate rectilinear motion barrel 32 moves along the optical axis in unison with the first intermediate rotary barrel 31.

The first intermediate rectilinear motion barrel 32 has straight advance grooves 32 s, through grooves 32 k, and cam grooves 32 c formed in an inner periphery (inner peripheral surface) thereof, and rectilinear slide key portions 32 t projecting from an outer periphery thereof. The first intermediate rectilinear motion barrel 32 has the rectilinear slide key portions 32 t for engagement with the respective straight advance grooves 23 s in the fixed barrel 23, so that the first intermediate rectilinear motion barrel 32 is rectilinearly guided. It should be noted that the each groove 32 k is substantially identical in track to each cam groove 32 c.

The first intermediate rotary barrel 31 has drive pins 31 d and cam pins 31 f projecting from an outer periphery thereof and straight advance grooves 31 s formed in an inner peripheral surface thereof. The drive pins 31 d are engaged with the respective straight advance grooves 22 s on the rotary barrel 22 through the respective through grooves 32 k, so that the first intermediate rotary barrel 31 performs rotation along with the rotary barrel 22. The cam pins 31 f are engaged with the respective cam grooves 23 c on the fixed barrel 23, so that the first intermediate barrel unit 30 moves in the optical axis direction following the respective tracks of the cam grooves 23 c.

FIG. 8 is an exploded perspective view of a second intermediate barrel unit 40 of the lens barrel shown in FIG. 4.

The second intermediate barrel unit 40 as a second stage of the lens barrel is identical in construction to the first intermediate barrel unit 30, and is comprised of a second intermediate rotary barrel (rotary member) 41 and a second intermediate rectilinear motion barrel (rectilinearly moving member) 42.

The second intermediate rectilinear motion barrel 42 has a projection 42 b for engagement with a groove portion 41 b (see FIG. 1) formed circumferentially on the inner periphery of the second intermediate rotary barrel 41, so that the intermediate rectilinear motion barrel 42 moves along the optical axis in unison with the second intermediate rotary barrel 41.

The second intermediate rectilinear motion barrel 42 has straight advance grooves 42 s, through grooves 42 k, and cam grooves 42 c formed on an inner peripheral surface thereof, and rectilinear slide key portions 42 t projecting from an outer periphery thereof. The second intermediate rectilinear motion barrel 42 has the rectilinear slide key portions 42 t for engagement with the straight advance grooves 32 s on the first intermediate rectilinear motion barrel 32, so that the second intermediate rectilinear motion barrel 42 is rectilinearly guided.

The second intermediate rotary barrel 41 has drive pins 41 d and cam pins 41 f projecting from an outer periphery thereof and straight advance grooves 41 s formed on an inner peripheral surface thereof. The drive pins 41 d are engaged with the respective straight advance grooves 31 s on the first intermediate rotary barrel 31 through the respective through grooves 32 k, so that the second intermediate rotary barrel 41 performs rotation along with the first intermediate rotary barrel 31. The cam pins 41 f are engaged with the respective cam grooves 32 c on the first intermediate rectilinear motion barrel 32, so that the second intermediate barrel unit 40 moves in the optical axis direction following the respective tracks of the cam grooves 32 c.

FIG. 9 is an exploded perspective view of a cam barrel unit of the lens barrel shown in FIG. 4.

The cam barrel unit 50 as a third stage of the lens barrel is comprised of a third intermediate rotary barrel 51, a cam barrel 52, an inner rectilinear motion barrel 53, and an inner rectilinearly moving plate 54.

The cam barrel 52 is formed with cams for controlling the motion of the first to third groups lenses 11 to 13 in the optical axis direction, and rotates around the optical axis.

The inner rectilinear motion barrel 53 is fitted in the cam barrel 52 and serves a rectilinear motion barrel for rectilinearly guiding the first to third groups lenses 11 to 13. Further, the inner rectilinearly moving plate 54 is guided by the second intermediate rectilinear motion barrel 42 disposed around the inner rectilinear motion barrel 53 as a rectilinear motion guide member, and serves as a rectilinear motion member connected to the rectilinear motion barrel. The rectilinear motion barrel and the rectilinear motion member form a rectilinear motion guide unit that rectilinearly guides a lens unit.

The cam barrel 52 is sandwiched from the front and rear in the optical axis direction by the rectilinear motion guide unit, and is movable together therewith in the optical axis direction.

The inner rectilinear motion barrel 53 has an inner peripheral surface thereof formed with projections (connecting portion) 53 a, a straight advance groove 53 s 2 for rectilinearly guiding the second group holder 72 (see FIG. 4), and a straight advance groove 53 s 3 for rectilinearly guiding the third group holder 73 (see FIG. 4). Further, the inner rectilinear motion barrel 53 has an outer periphery thereof formed with rectilinear slide key portions (rectilinear motion guide portion) 53 t on an object-side end face thereof for rectilinearly guiding a first group barrel unit 60 (see FIG. 4). The inner rectilinearly moving plate 54 has an inner periphery thereof formed with projections 54 a and rectilinear slide key portions 54 t.

The inner rectilinear motion barrel 53 is fitted in the cam barrel 52 from the front thereof, and the inner rectilinearly moving plate 54 is fitted into the cam barrel 52 from the rear thereof, such that the cam barrel 52 is sandwiched by the inner rectilinear motion barrel 53 and the inner rectilinearly moving plate 54. The projections 53 a of the inner rectilinear motion barrel 53 are engaged with the respective associated projections 54 a of the inner rectilinearly moving plate 54, whereby the inner rectilinear motion barrel 53 and the inner rectilinearly moving plate 54 are secured in a state sandwiching the cam barrel 52 therebetween and rectilinearly guided.

The inner rectilinearly moving plate 54 is rectilinearly guided by engagement between the rectilinear slide key portions 54 t and the respective associated straight advance grooves 42 s of the second intermediate rectilinear motion barrel 42. The inner rectilinearly moving plate 54 is rectilinearly guided, whereby the inner rectilinear motion barrel 53 is also rectilinearly guided.

Further, the cam barrel 52 has drive pins 52 d and cam pins 52 f projecting from an outer periphery thereof. The drive pins 52 d are engaged with the respective straight advance grooves 41 s of the second intermediate rotary barrel 41 through the respective through grooves 42 k, whereby the cam barrel 52 rotates in unison with the second intermediate rotary barrel 41. The cam pins 52 f are engaged with the respective cam grooves 42 c of the second intermediate rectilinear motion barrel 42, whereby the cam barrel unit 50 is moved along the optical axis following the respective tracks of the cam grooves 42 c.

The third intermediate rotary barrel 51 and the cam barrel 52 rotate in unison by engagement between engagement portions 51 a of the third intermediate rotary barrel 51 and projections 52 a of the can cylinder 52.

Further, the cam barrel 52 has a cam 52 c 1 formed on the outer peripheral surface thereof for controlling the distance of travel of the first group barrel unit 60, and cams 52 c 2 and 52 c 3 formed on an inner peripheral surface thereof for controlling the distance of travel of the second group holder 72 and that of a third group holder 73, respectively.

The first group barrel unit 60 appearing in FIG. 4 is comprised of the first group barrel 61, a first group cover 62, and barrier blades 63 as shown in FIG. 1. The first group barrel 61 has a straight advance groove 61 s formed on an inner peripheral surface thereof for engagement with the rectilinear slide key portions 53 t of the inner rectilinear motion barrel 53, so that the first group barrel unit 60 is rectilinearly guided. The rectilinear slide key portions 53 t restrict the motion of the cam barrel 52 in the optical axis direction.

The first group barrel 61 servers as a first lens holding member that holds the first group lens 11. Further, the first group cover 62 servers as a second lens holding member that holds the second group lens 12.

Further, the first group barrel 61 has a cam pin 61 f for engagement with the cam 52 c 1 of the cam barrel 52. Therefore, the first group barrel unit 60 moves in the optical axis direction following the tracks of the cam 52 c 1. The barrier blades 63 are operated by a drive means, not shown, for being opened for the use of the lens barrel, and closed when the lens barrel is retracted.

As described above, in the lens barrel (lens barrel unit) 2 in the present embodiment, the rotary barrel 22 is rotated by the driving force of the motor 81, whereby the first intermediate rotary barrel 31, the second intermediate rotary barrel 41, the cam barrel 52, and the third intermediate rotary barrel 51 in engagement with the rotary barrel 22 are rotated in unison.

Further, the fixed barrel 23 and the first intermediate rectilinear motion barrel 32, the second intermediate rectilinear motion barrel 42, the inner rectilinearly moving plate 54, and the inner rectilinear motion barrel 53 in engagement with the fixed barrel 23 are rectilinearly guided, whereby the first group barrel unit 60, the second group holder 72, and the third group holder 73 are rectilinearly guided.

The lens barrel comprised of the above-described components is mounted to an image pickup apparatus. FIG. 5 shows the image pickup apparatus equipped with the four-stage retractable lens barrel 2.

FIG. 10 is an unfolded view showing the inner peripheral surface of the fixed barrel appearing in FIG. 6. FIG. 11 is an unfolded view showing the inner peripheral surface of the first intermediate rectilinear motion barrel appearing in FIG. 7. FIG. 12 is an unfolded view showing the inner peripheral surface of the second intermediate rectilinear motion barrel appearing in FIG. 8. Further, FIG. 13 is an unfolded view showing the inner peripheral surface of the cam barrel appearing in FIG. 9. In each of the figures, only essential parts are shown.

As shown in FIG. 10, the fixed barrel 23 has the inner peripheral surface formed with the straight advance grooves 23 s, the through grooves 23 k, and the cam grooves 23 c. The through grooves 23 k and the associated cam grooves 23 c are identical in track, and each through groove 23 k is a through groove for engagement between the associated drive pin 31 d of the first intermediate rotary barrel 31 and the associated straight advance groove 22 s of the rotary barrel 22.

The cam groove 23 c is engaged with the associated cam pin 31 f of the first intermediate rotary barrel 31. The cam pin 31 f is shifted to a position 23W when the lens barrel enters the wide-angle state, while when the lens barrel enters the telephoto state, the cam pin 31 f is shifted to a position 23T.

As shown in FIG. 11, the first intermediate rectilinear motion barrel 32 has the inner peripheral surface thereof formed with the straight advance grooves 32 s, the through grooves 32 k, and the cam grooves 32 c. The through grooves 32 k and the associated cam grooves 32 c are identical in track, and each through groove 32 k is a through groove for engagement between the associated drive pin 41 d of the second intermediate rotary barrel 41 and the associated straight advance groove 31 s of the first intermediate rotary barrel 31.

The cam groove 32 c is engaged with the associated cam pin 41 f of the second intermediate rotary barrel 41. The cam pin 41 f is shifted to a position 32W when the lens barrel enters the wide-angle state, while when the lens barrel enters the telephoto state, the cam pin 41 f is shifted to a position 32T.

Although in the present embodiment, the inner cam grooves of the fixed barrel 23 and those of the first intermediate rectilinear motion barrel 32 are formed to have the substantially identical shape, they may be formed to have different shapes insofar as the relationship between a cam groove, a through groove, and a straight advance groove can be satisfied.

As shown in FIG. 12, the second intermediate rectilinear motion barrel 42 has the inner peripheral surface thereof formed with the straight advance grooves 42 s, the through grooves 42 k, and the cam grooves 42 c. The through grooves 42 k and the associated cam grooves 42 c are identical in track, and each through groove 42 k is for engagement between the associated drive pin 52 d of the cam barrel 52 and the associated straight advance groove 41 s of the second intermediate rotary barrel 41.

The cam groove 42 c is engaged with the associated cam pin 52 f of the cam barrel 52. The cam pin 52 f is shifted to a position 42W when the lens barrel enters the wide-angle state, while when the lens barrel enters the telephoto state, the cam pin 52 f is shifted to a position 42T. The second intermediate rectilinear motion barrel 42 is configured to always guide the inner rectilinearly moving plate 54 rectilinearly by the six straight advance grooves 42 s.

As shown in FIG. 13, the cam barrel 52 has the inner peripheral surface thereof formed with the cam 52 c 2 for controlling the distance of travel of the second group holder 72 and the cam 52 c 3 for controlling the distance of travel of the third group holder 73. The cam 52 c 2 is engaged with a cam pin 72 f (see FIG. 1) of the second group holder 72.

On the other hand, the cam 52 c 3 is engaged with a cam pin 73 f (see FIG. 1) of the third group holder 73. The cam pins 72 f and 73 f are shifted to respective positions 52 c 2W and 52 c 3W when the lens barrel enters the wide-angle state, while when the lens barrel enters the telephoto state, the cam pins 72 f and 73 f are shifted to respective positions 52 c 2T and 52 c 3T.

Since the cam barrel 52 is disposed, as described hereinbefore, in a manner sandwiched in the optical axis direction between the inner rectilinear motion barrel 53 and the inner rectilinearly moving plate 54 disposed radially inward of the cam barrel 52, for serving as a rectilinearly moving guide for guiding the lens unit, the inner rectilinear motion barrel 53 and the inner rectilinearly moving plate (rectilinearly moving member) 54 are moved in unison as the cam barrel moves along the optical axis.

For this reason, the cam barrel 52 is not required to have a bayonet connection structure which is employed for connection between the first intermediate rotary barrel 31 and the first intermediate rectilinear motion barrel 32. Therefore, as shown in FIG. 13, the cams can be arranged on the inner peripheral surface of the cam barrel 52 such that a length 52B of the cam barrel 52 in the optical axis direction is minimized.

Although in the present embodiment, the cam grooves and the through grooves are shaped as shown in FIGS. 10 to 13, this is not limitative, but they can be shaped as desired insofar as the relationship between each cam groove, each through groove, and each straight advance groove can be satisfied.

Further, in the present embodiment, the two intermediate barrel units (the first intermediate barrel unit 30 and the second intermediate barrel unit 40) are arranged to form the four-stage retractable lens barrel, but this is not limitative. For example, if only one intermediate barrel unit is used, it is possible to form a three-stage retractable lens barrel.

Further, if three intermediate barrel units are used, it is possible to form a five-stage retractable lens barrel. By thus changing the number of intermediate barrel units, the number of stages of a lens barrel can be changed as desired.

In the following, a description will be given of a second embodiment of the present invention.

FIG. 14 is a view of a lens barrel of an image pickup apparatus according to the second embodiment, which is in the wide-angle state when the image pickup apparatus is in the shooting mode. FIG. 15 is an exploded perspective view of a fixed barrel and a gear unit of the lens barrel, and FIG. 16 is an exploded perspective view of a first intermediate barrel unit of the lens barrel.

In the present embodiment, photographic lens units (a first group lens 11 to a fourth group lens 14), a second intermediate barrel unit 40, a cam barrel unit 50, and a first group barrel unit 60 have the same construction as in the first embodiment.

Now, a description will be given of each stage of the lens barrel.

Referring to FIG. 15, the fixed barrel 123 is secured to the camera body 1 e.g. with screws, together with the holder 24 for holding the image pickup element 15, and is held thereat.

In the present embodiment, a zoom gear unit 180 is comprised of a motor 181 as a drive source, gears 182 to 186 for transmitting a driving force from the motor 181, and a long gear 187, and the long gear 187 is held by a gear holding part 123 n of the fixed barrel 123. Further, the fixed barrel 123 has an inner peripheral surface thereof formed with straight advance grooves 123 s and cam grooves 123 c.

As shown in FIG. 16, a first intermediate barrel unit 130 as a first stage of the lens barrel is comprised of a first intermediate rotary barrel 131 and a first intermediate rectilinear motion barrel 132. The first intermediate rectilinear motion barrel 132 has a projection 132 b projecting therefrom for engagement with a groove portion 131 b (see FIG. 14) formed circumferentially on the inner periphery of the first intermediate rotary barrel 131, so that the first intermediate rectilinear motion barrel 132 moves along the optical axis in unison with the first intermediate rotary barrel 131.

The first intermediate rectilinear motion barrel 132 has straight advance grooves 132 s, through grooves 132 k, and cam grooves 132 c formed on an inner peripheral surface thereof, and rectilinear slide key portions 132 t projecting from an outer periphery thereof, as in the first embodiment. The first intermediate rectilinear motion barrel 132 has the rectilinear slide key portions 132 t for engagement with the straight advance grooves 123 s on the fixed barrel 123, so that the first intermediate rectilinear motion barrel 132 is rectilinearly guided.

The first intermediate rotary barrel 131 has a drive gear 131 g and cam pins 131 f projecting from an outer peripheral surface thereof and straight advance grooves 131 s formed on an inner peripheral surface thereof. The drive gear 131 g is engaged with the long gear 187, and hence the first intermediate rotary barrel 131 performs rotation. The cam pins 131 f are engaged with the respective cam grooves 123 c on the fixed barrel 123, so that the first intermediate barrel unit 130 moves in the optical axis direction following the respective tracks of the cam grooves 123 c.

The second intermediate barrel unit 40 as a second stage of the lens barrel, the cam barrel unit 50 as a third stage of the lens barrel, and the first group barrel unit 60 have the same construction as in the first embodiment.

FIG. 17 is an unfolded view showing the inner peripheral surface of the fixed barrel appearing in FIG. 15, and FIG. 18 is an unfolded view showing the inner peripheral surface of the first intermediate rectilinear motion barrel appearing in FIG. 16. In each of the figures, only essential parts are shown.

As shown in FIG. 17, the fixed barrel 123 has the inner peripheral surface thereof formed with the straight advance grooves 123 s, the cam grooves 123 c, and the gear holding part 123 n. The cam groove 123 c is engaged with the associated cam pin 131 f of the first intermediate rotary barrel 131. The cam pin 131 f is shifted to a position 123W when the lens barrel enters the wide-angle state, while when the lens barrel enters the telephoto state, the cam pin 131 f is shifted to a position 123T.

As shown in FIG. 18, the first intermediate rectilinear motion barrel 132 has the inner peripheral surface thereof formed with the straight advance grooves 132 s, the through grooves 132 k, and the cam grooves 132 c. Each through groove 132 k is for engagement between the associated drive pin 41 d of the second intermediate rotary barrel 41 and the associated straight advance groove 131 s of the first intermediate rotary barrel 131.

The cam groove 132 c is engaged with the associated cam pin 41 f of the second intermediate rotary barrel 41. The cam pin 41 f is shifted to a position 132W when the lens barrel enters the wide-angle state, while when the lens barrel enters the telephoto state, the cam pin 41 f is shifted to a position 132T.

Although in the present embodiment, the inner cam grooves of the fixed barrel 123 and those of the first intermediate rectilinear motion barrel 132 are formed to have respective shapes substantially identical in track, they may be configured differently insofar as the relationship between each cam groove, each through groove, and each straight advance groove can be satisfied. Further, the cam grooves may be configured to formed on side walls of through grooves.

Further, in the present embodiment as well as in the first embodiment, the two intermediate barrel units are arranged so as to form the four-stage retractable lens barrel, but this is not limitative. For example, if only one intermediate barrel unit is used, it is possible to form a three-stage retractable lens barrel.

Further, if three intermediate barrel units are arranged, it is possible to form a five-stage retractable lens barrel. By thus changing the number of intermediate barrel units, the number of stages of a lens barrel can be changed as desired.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions.

This application claims priority from Japanese Patent Application No. 2008-203184 filed Aug. 6, 2008, which is hereby incorporated by reference herein in its entirety. 

1. An image pickup apparatus comprising: a lens unit; a rectilinear motion guide unit that is restricted to rotate around the optical axis of said lens unit; a rectilinear motion member that is restricted to rotate around the optical axis by engagement with said rectilinear motion guide unit; a rectilinear motion barrel that is restricted to rotate around the optical axis by connecting with said rectilinear motion member, wherein the rectilinear motion barrel guides said lens unit rectilinearly; and a cam barrel that is sandwiched from front and rear in a direction along the optical axis by said rectilinear motion member and said rectilinear motion barrel, wherein the cam barrel is formed with a cam for controlling motion of said lens unit along the optical axis, wherein the cam barrel is movable together with said rectilinear motion member and said rectilinear motion barrel along the optical axis by the sandwich of said rectilinear motion member and said rectilinear motion barrel.
 2. The image pickup apparatus according to claim 1, further comprising a first lens holding member that holds a first lens unit, said first lens holding member being engaged with a cam provided on an outer periphery of said cam barrel, and a second lens holding member that holds a second lens unit, said second lens holding member being engaged with a cam provided on an inner periphery of said cam barrel, and wherein said first lens holding member and said second lens holding member are rectilinearly guided by said rectilinear motion barrel disposed on the inner periphery of said cam barrel.
 3. The image pickup apparatus according to claim 2, wherein said rectilinear motion barrel has a rectilinear motion guide portion provided on an object-side end face thereof, said rectilinear motion guide portion rectilinearly guiding said first lens holding member, and at the same time restricting motion of said cam barrel along the optical axis.
 4. The image pickup apparatus according to claim 1, wherein said rectilinear motion barrel has a connecting portion on an inner periphery thereof, said connecting portion being connected to said rectilinear motion member.
 5. The image pickup apparatus according to claim 2, further comprising a rotary barrel disposed around said first lens holding member, said rotary barrel being connected to said cam barrel and being configured to rotate in unison therewith. 